This proposal addresses the problem of how to target gene therapy vectors to enhance efficacy and minimize toxicity. We have developed a strategy for genetic selection of ligands that are suitable for gene delivery via cell surface receptors. The selection is based on the ability of a ligand targeted phage vector to deliver a reporter gene, GFP, to mammalian cells that express the appropriate cell surface receptor. We recover the ligand display phage from genetically transduced GFP expressing cells using FACS. Using this strategy, we can enrich an EGF display phage 1 million fold after 3-4 rounds of selection on receptor bearing cells. Here, we propose to further develop this technology by demonstrating selection of peptide ligands that target the FGF receptor from random peptide libraries. Targeting ligands will be enriched by repeated rounds of selection on FGF receptor overexpressing cells. The goal is to develop a strategy to identify gene transfer ligands for any receptor that can be functionally overexpressed in COS cells. The long term goal is to develop a technology platform for identifying targeting ligands that can be attached genetically to viral gene therapy vectors or incorporated directly into non-viral vectors for therapeutic gene delivery. PROPOSED COMMERCIAL APPLICATIONS: We propose to develop a new method of identifying novel targeting peptides to improve existing gene delivery vehicles by increasing the specificity of vector targeting for specific cell types, thus increasing efficacy and reducing toxicity. The commercial application of the newly discovered ligands will be to target adenovirus vectors and non-viral vectors for therapeutic gene delivery. Moreover, this technology has broad potential as a platform for identifying new gene and drug delivery agents that target specific cell surface receptors.